Piston assemblies for engaging transmission clutches are known in the art. Typical rotating wet clutches for automobile transmissions include a closed fluid circuit for actuating a piston with respect to a centrifugal pressure compensation dam. A spring element, commonly a diaphragm spring or a package of coil springs, is usually situated between the piston and dam in order to return the piston to its fully open position when the piston chamber is depressurized, at which open position the clutch is disengaged. Typically, these systems are installed by first placing the piston in place, adding the return spring, then pressing the compensation dam against the spring to pre-load the spring, and finally installing a snap ring to hold the compensation dam in position to maintain the pre-loaded condition of the spring.
Although a common method of constructing a clutch system, snap rings continue to have a tendency to seat improperly when installed, and such improper seating is often not immediately identifiable. In some cases, improper seating of a snap ring may not be identified until later assembly steps, until the assembly is fully completed and finally tested, or even until it fails in the field after installation of the transmission in an automobile. That is, an improperly seated ring may dislodge and cause a loss of proper transmission function. U.S. Pat. No. 5,911,295 (Itonaga et al.), U.S. Pat. No. 5,893,445 (Dover), and U.S. Pat. No. 5,653,322 (Vasa et al.) are hereby incorporated by reference in their entireties. These patents each teach examples of conventional transmission clutch assemblies which include snap rings and return springs of various types.